A television system with an aspect ratio of 16:9, i.e. a picture frame with a relatively greater horizontal dimension than the existing frame with an aspect ratio of 4:3, is now being implemented commercially and some solid image sensors compatible with both systems have been developed.
An exemplary solid state image sensor compatible with the two systems is illustrated in FIG. 1. This solid state image sensor comprises an imaging region 1 consisting of a matrix of photosensitive elements (not shown) and a plurality of vertical shift registers (not shown) disposed adjacent to columns of said photosensitive elements and corresponding to an aspect ratio of 16:9, three horizontal shift registers 5, 6, 7 and three buffer amplifiers 8, 9 and 10 connected to said horizontal shift registers 5, 6 and 7, respectively. The imaging region 1 is divided into three segments, viz. a first segment 2 corresponding to an aspect ratio of 4:3, a second segment 3 and a third segment 4 which are not required for said aspect ratio of 4:3 but are required for said aspect ratio of 16:9, and the three horizontal shift registers 5, 6 and 7 are disposed in correspondence with said segments 2, 3 and 4, respectively. Indicated by A1, A2, A3 and A4 are terminals for supplying driving pulses to transfer gate electrodes of the vertical shift registers. The arrowmarks indicate the direction of flow of signal charges.
The method of driving the above solid state image sensor is now described.
For both aspect ratios of 4:3 and 16:9, signal charges are read out from the imaging region 1 to the vertical shift registers in the first place. Then, vertical transfer signals are applied to the vertical shift registers from terminals A1-A4 to transfer the signal charges accumulated in the groups of photosensitive elements in said first segment 2, second segment 3 and third segment 4 to said first horizontal shift register 5, second horizontal shift register 6 and third horizontal shift register 7, respectively. Then, horizontal transfer pulses are applied to the respective horizontal shift registers to transfer the signal charges therein to the corresponding buffer amplifiers 8, 9 and 10 to thereby output picture signals. In the described arrangement, a picture signal corresponding to the aspect ratio of 4:3 is available from the buffer amplifier 8 and a picture signal for the aspect ratio of 16:9 is obtained by superimposing the signal outputs of the buffer amplifiers 8, 9 and 10 in an external circuit.
However, this prior art solid state image sensor is complicated in construction because each of the horizontal transfer and buffer amplifier stages has been divided into three segments. Moreover, in order to obtain a picture signal corresponding to an aspect ratio of 16:9, signal outputs of the three buffer amplifiers must be superimposed and this requirement adds complexity to the signal processing and driving circuitry.